Non-aqueous electrolyte secondary battery

ABSTRACT

A non-aqueous electrolyte secondary battery, in which a positive electrode includes a positive electrode mixture layer in which a mixture containing a positive electrode active material is formed and a positive electrode mixture layer non-forming portion in which the positive electrode mixture layer is not formed, and a negative electrode includes a negative electrode mixture layer in which a mixture containing a negative electrode active material is formed and a negative electrode mixture layer non-forming portion in which the negative electrode mixture layer is not formed. At least one of the positive electrode mixture layer non-forming portion and the negative electrode mixture layer non-forming portion has a resin portion substantially formed of a swellable resin having a property of swelling the non-aqueous electrolyte.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2020-155589 filed on Sep. 16, 2020, incorporated herein by reference inits entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a non-aqueous electrolyte secondarybattery. Specifically, the present disclosure relates to a non-aqueouselectrolyte secondary battery having a resin portion formed of aswellable resin on a current collector.

2. Description of Related Art

A non-aqueous electrolyte secondary battery, such as a lithium-ionsecondary battery, is lightweight and has a high energy density ascompared with the existing batteries. Therefore, in recent years, such anon-aqueous electrolyte secondary battery is used as a power sourcemounted on a vehicle using an electricity as a drive source, or a powersource mounted on an electronic product, such as a personal computer, amobile terminal. In particular, the lithium-ion secondary battery thatis lightweight and has a high energy density is preferably used as ahigh-output power source for driving a vehicle, such as an electricvehicle (EV), a plug-in hybrid vehicle (PHV), or a hybrid vehicle (HV).

By the way, the non-aqueous electrolyte secondary battery used as thepower source for driving the vehicle needs to be charged or dischargedwith a large current in a short time. Therefore, the power source fordriving the vehicle is requested to have excellent rapid charge anddischarge characteristic (that is, high rate characteristic). Further,the non-aqueous electrolyte secondary battery needs to be mounted on thevehicle and continuously exhibit stable performance even in a case wherethe charge and discharge cycle is repeated for a long period of time.Therefore, the power source for driving the vehicle is requested to haveexcellent durability against the rapid charge and discharge (that is,high rate resistance).

Various approaches have been attempted to improve these characteristics.One such approach is to improve a separator sheet used in thenon-aqueous electrolyte secondary battery. Japanese Unexamined PatentApplication Publication No. 2016-115593 (JP 2016-115593 A) discloses atechnique of increasing an amount of the non-aqueous electrolyte held ina center portion of a wound electrode body and suppressing thetemperature rise of the center portion of the wound electrode body byadjusting a solubility parameter of a binder contained in the heatresistant layer disposed on the separator sheet.

SUMMARY

By the way, in a case where a high rate charge and discharge cycle isapplied to the non-aqueous electrolyte secondary battery that includes asheet-shaped electrode body, the temperatures of the electrode body andthe non-aqueous electrolyte held in the electrode body rise. In a casewhere the temperature of the non-aqueous electrolyte rises, a part ofthe non-aqueous electrolyte flows out of the electrode body due tothermal expansion, and as a result, the internal resistance may beincreased and the high rate resistance may be decreased. By suppressingthe temperature rise of the center portion of the wound electrode body,the amount of the non-aqueous electrolyte held in the center portion canbe improved, but the outflow of the non-aqueous electrolyte from the endportion cannot be sufficiently suppressed. Further development oftechnique is desired in order to improve the high rate resistance of thenon-aqueous electrolyte secondary battery.

The present disclosure provides a non-aqueous electrolyte secondarybattery having excellent high rate resistance.

The present inventors have found that in a case where a portion in whicha mixture containing an active material corresponding to a positiveelectrode and a negative electrode is formed on a current collector isdefined as a mixture layer, by forming a resin portion formed of a resinhaving a property of swelling the non-aqueous electrolyte (hereinafter,referred to as swellable resin) in a portion in which the mixture is notformed (hereinafter, referred to as mixture layer non-forming portion),the temperature rise of the end portion of the electrode body can besuppressed. Further, the present inventors have found that thenon-aqueous electrolyte can be suitably held in the electrode body bysuppressing the temperature rise in the end portion of the electrodebody, and as a result, the high rate resistance can be improved.

That is, a non-aqueous electrolyte secondary battery according to anaspect of the present disclosure includes an electrode body, and anon-aqueous electrolyte. The electrode body has a structure in which aplurality of positive electrodes and negative electrodes are stacked viaa separator. The positive electrode includes a positive electrodemixture layer in which a mixture containing a positive electrode activematerial is formed and a positive electrode mixture layer non-formingportion in which the positive electrode mixture layer is not formed. Thenegative electrode includes a negative electrode mixture layer in whicha mixture containing a negative electrode active material is formed anda negative electrode mixture layer non-forming portion in which thenegative electrode mixture layer is not formed. At least one of thepositive mixture layer non-forming portion and the negative electrodemixture layer non-forming portion has a resin portion substantiallyformed of a swellable resin having a property of swelling thenon-aqueous electrolyte.

With such a configuration, a thermal capacity of the end portion of theelectrode body can be increased, and as a result, the high rateresistance of the non-aqueous electrolyte secondary battery can beimproved.

The resin portion may be formed along the corresponding mixture layer.With such a configuration, the thermal capacity of the end portion ofthe electrode body can be more uniformly improved, and the effect of thetechnique disclosed herein can be exhibited at a higher level.

A thermal capacity of the resin portion may be 10 J/(kg·K) or more perunit weight (kg) of the corresponding mixture layer. With such aconfiguration, the thermal capacity of the end portion of the electrodebody can be suitably increased, and the high rate resistance of thenon-aqueous electrolyte secondary battery can be improved.

The resin portion may contain polyvinylpyrrolidone, styrene-butadienerubber, and an acrylic resin. By containing a resin having high swellingproperty in the resin portion, the thermal capacity of the end portionof the electrode body can be more suitably increased, and the high rateresistance of the non-aqueous electrolyte can be improved.

The resin portion may be formed at least in the negative electrodemixture layer non-forming portion. By providing the resin portion on thenegative electrode side in which the non-aqueous electrolyte is likelyto flow out from the electrode due to the temperature rise as comparedwith the positive electrode side, the effect of the technique disclosedherein can be exhibited at a higher level.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a cross-sectional view schematically showing a configurationof a non-aqueous electrolyte secondary battery according to anembodiment;

FIG. 2 is a schematic view showing an example of a configuration of awound electrode body of the non-aqueous electrolyte secondary batteryaccording to the embodiment; and

FIG. 3 is a plan view schematically showing configurations of a positiveelectrode and a negative electrode of the non-aqueous electrolytesecondary battery according to the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a suitable embodiment of a non-aqueous electrolytesecondary battery disclosed herein will be described with reference tothe drawings as appropriate, using a lithium-ion secondary battery as anexample.

Needless to say, the following embodiment is not intended toparticularly limit the technique disclosed herein.

The non-aqueous electrolyte secondary battery disclosed herein is notlimited to the lithium-ion secondary battery described below, and asodium ion secondary battery, a magnesium ion secondary battery, or alithium-ion capacitor (included in a so-called physical battery) is alsoa typical example included in the non-aqueous electrolyte secondarybattery referred to here.

Further, although the lithium-ion secondary battery including a woundelectrode body having a structure in which a plurality of electrodebodies of positive electrodes and negative electrodes are wound via aseparator will be described here, the electrode body is not limited tosuch a configuration, and may have a configuration in which theelectrode bodies of the positive electrodes and the negative electrodesare stacked via the separator.

Matters other than those specifically mentioned in the presentspecification, and needed for carrying out the present disclosure can begrasped as design matters of those skilled in the art based on therelated art in the field. The present disclosure can be carried outbased on the contents disclosed in the present specification and commongeneral technical knowledge in the field.

Further, in a case where the numerical range is described as A to B(here, A and B are any numerical values) in the present specification,it means A or more and B or less.

In the drawings below, the members and the portions that perform thesame effects are designated by the same reference numerals, andduplicate descriptions may be omitted or simplified. Further, thedimensional relationship (length, width, and the like) in the drawingsbelow does not always reflect the actual dimensional relationship, anddoes not limit the configuration of the secondary battery at all.

In the present specification, the term “swellable resin” refers to aresin in which a specific thermal capacity is increased by absorbing anon-aqueous electrolyte used in the non-aqueous electrolyte secondarybattery. For example, there is a resin in which the specific thermalcapacity is increased as compared with before the resin swells thenon-aqueous electrolyte in a case where the resin swells the non-aqueouselectrolyte obtained by mixing ethylene carbonate (EC), ethyl methylcarbonate (EMC), and dimethyl carbonate (DMC) at a volume ratio of30:40:30, and dissolving LiPF₆ as a supporting salt at a concentrationof 1.0 mol/L. The swelling with the non-aqueous electrolyte can beperformed, for example, by immersing the resin in the non-aqueouselectrolyte at room temperature for about several tens of minutes toseveral hours.

In the present specification, “substantially formed of swellable resin”means the resin portion mainly formed of the swellable resin, and atrace component is allowed to be mixed as long as the effects of thepresent disclosure are not significantly impaired. Further, theswellable resin that forms the resin portion is not limited to one type,and the resin portion may be formed of a plurality of types. A contentratio of the swellable resin in the resin portion is, for example,preferably 90% by weight or more, more preferably 95% by weight or more,and still more preferably 98% by weight or more.

In the present application, the specific thermal capacity is representedby the specific thermal capacity at 25° C. measured based on adifferential scanning calorimetry (DSC) method. The measurement iscarried out in a dry nitrogen atmosphere, sapphire (Al₂O₃) is used as astandard sample, and an aluminum vessel is used as a sample vessel. Thespecific thermal capacity of the resin before and after being swellingthe non-aqueous electrolyte can be measured by using a sample weightbefore swelling the non-aqueous electrolyte.

Schematic diagrams of the lithium-ion secondary battery according to theembodiment are shown in FIGS. 1 to 3. As shown in FIG. 1, a lithium-ionsecondary battery 100 has a configuration in which a flat woundelectrode body 40 is accommodated in a flat square battery case 20together with a non-aqueous electrolyte 80 as shown in FIG. 2. At leasta part of the non-aqueous electrolyte 80 is impregnated in the woundelectrode body 40. As shown in FIG. 3, at least any one of a positiveelectrode 50 and a negative electrode 60 that configure the woundelectrode body 40 includes a resin portion 62 a (52 a) in a part of amixture layer non-forming portion 62 (52).

As shown in FIG. 1, the battery case 20 that configures the lithium-ionsecondary battery 100 has a case main body 21 having an opening and alid 22 for closing the opening. The lid 22 is provided with a positiveelectrode terminal 23 and a negative electrode terminal 24 for externalconnection, and a safety valve 30 that has a thin wall and is set torelease an internal pressure of the battery case 20 in a case where theinternal pressure rises a predetermined level or more. The positiveelectrode terminal 23 and the negative electrode terminal 24 areelectrically connected to a positive electrode current collector plate25 and a negative electrode current collector plate 26, respectively.Examples of the material of the battery case 20 include a lightweightmetal material having good thermal conductivity, such as aluminum.

The lithium-ion secondary battery 100 having such a configuration can beconstructed by, for example, accommodating the wound electrode body 40inside through the opening of the case main body 21, attaching the lid22 to the opening, injecting an appropriate amount of the non-aqueouselectrolyte 80 into the battery case 20 through the liquid injectionport 32, and then sealing the liquid injection port 32 with a sealingmaterial 33. The positive electrode current collector plate 25 and thenegative electrode current collector plate 26 are respectively welded toa positive electrode current collector 51 and a negative electrodecurrent collector 61 by resistance welding, ultrasonic welding, or thelike. In FIG. 1, reference numerals 25 a, 26 a each indicate the weldedportion.

As shown in FIG. 2, the wound electrode body 40 has a configuration inwhich the sheet-shaped positive electrode 50 in which a positiveelectrode mixture layer 53 is formed on one side or both sides of thelong positive electrode current collector 51 along a longitudinaldirection and the sheet-shaped negative electrode 60 in which a negativeelectrode mixture layer 63 is formed on one side or both sides of thelong negative electrode current collector 61 along the longitudinaldirection are overlapped with each other via two long separators 72, 74and wound in the longitudinal direction. Further, the wound electrodebody 40 includes the positive electrode mixture layer non-formingportion 52 and the negative electrode mixture layer non-forming portion62 to protrude outward from both ends of a winding axis WL.

Normally, a width b1 of the negative electrode mixture layer 63 isdesigned to be wider than a width a1 of the positive electrode mixturelayer 53. Further, normally, widths c1, c2 of the separators 72, 74 aredesigned to be wider than the width b1 of the negative electrode mixturelayer 63 (c1, c2>b1>a1).

As shown in FIG. 3, in at least one of the positive electrode 50 and thenegative electrode 60, the mixture layer non-forming portion has theresin portion substantially formed of the swellable resin having aproperty of swelling the non-aqueous electrolyte. By disposing theswellable resin in the mixture layer non-forming portion, the thermalcapacity of the end portion of the electrode body can be increased, andthe temperature rise of the end portion of the electrode body can besuppressed. As a result, the non-aqueous electrolyte is suitably held inthe electrode body, and the high rate resistance of the lithium-ionsecondary battery 100 can be improved.

As the positive electrode current collector 51 and the positiveelectrode mixture layer 53 that configure the positive electrode 50, thesame positive electrode current collector and positive electrode mixturelayer used in the lithium-ion secondary battery in the related art canbe used without particular limitation.

Examples of the positive electrode current collector 51 include aluminumfoil. Examples of a positive electrode active material contained in thepositive electrode mixture layer 53 include a lithium transition metaloxide (LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂, LiNiO₂, LiCoO₂, LiFeO₂, LiMn₂O₄,LiNi_(0.5)Mn_(1.5)O₄, and the like) and a lithium transition metalphosphate compound (LiFePO₄ and the like). The positive electrodemixture layer 53 can contain components other than the active material,such as a conductive material or a binder. As the conductive material,for example, carbon black, such as acetylene black (AB), or other carbonmaterials (graphite and the like) can be suitably used. As the binder,polyvinylidene fluoride (PVDF), an acrylic binder, polyvinylpyrrolidone(PVP), and the like can be used. As the solvent, water or a mixedsolvent mainly formed of water can be preferably used, andN-methyl-2-pyrrolidone (NMP) and the like is suitably used.

A pasty positive electrode mixture (hereinafter referred to as “positiveelectrode mixture paste”) can be prepared by mixing the positiveelectrode active material, the conductive material, the binder, and thesolvent as described above by using a known mixing device. Examples ofthe mixing device include a planetary mixer, a homogenizer, clearmix,filmix, a bead mill, a ball mill, an extrusion kneader and the like.Further, in the present specification, “paste” is used as a termincluding the form called “slurry” and “ink”.

The application of the positive electrode mixture paste to the positiveelectrode current collector 51 can be performed according to a knownmethod. For example, the application can be performed by using a coatingdevice, such as a gravure coater, a comma coater, a slit coater, or adie coater.

The positive electrode mixture layer 53 can be formed by drying theapplied positive electrode mixture paste by a known method.Specifically, the positive electrode mixture layer 53 can be formed bydrying the positive electrode current collector 51 coated with thepositive electrode mixture paste in a hot air drying furnace, aninfrared drying furnace, or the like.

As the negative electrode current collector 61 and the negativeelectrode mixture layer 63 that configure the negative electrode 60, thesame negative electrode current collector and negative electrode mixturelayer used in the lithium-ion secondary battery in the related art canbe used without particular limitation.

Examples of the negative electrode current collector 61 include copperfoil. Examples of the negative electrode active material contained inthe negative electrode mixture layer 63 include a carbon material, suchas graphite, hard carbon, or soft carbon is used. Among the aboveexamples, graphite is preferable. The graphite may be natural graphiteor artificial graphite, or may be coated with an amorphous carbonmaterial. The negative electrode mixture layer 63 can contain componentsother than the active material, such as a binder or a thickener. As thebinder, styrene-butadiene rubber (SBR) and the like can be used. As thethickener, carboxymethyl cellulose (CMC) and the like can be used. Asthe solvent, an aqueous solvent is preferably used. The aqueous solventneed only have aqueous as a whole, and water or the mixed solvent mainlyformed of water can be preferably used.

A pasty negative electrode mixture (hereinafter referred to as “negativeelectrode mixture paste”) can be prepared by mixing the negativeelectrode active material, the conductive material, the binder, and thesolvent as described above by using a known mixing device. Examples ofthe mixing device include a planetary mixer, a homogenizer, clearmix,filmix, a bead mill, a ball mill, an extrusion kneader and the like.

The application of the negative electrode mixture paste to the negativeelectrode current collector 61 can be performed according to a knownmethod. For example, the application can be performed by using a coatingdevice, such as a gravure coater, a comma coater, a slit coater, or adie coater.

The negative electrode mixture layer 63 can be formed by drying theapplied negative electrode mixture paste by a known method.Specifically, the negative electrode mixture layer 63 can be formed bydrying the negative electrode current collector 61 coated with thenegative electrode mixture paste in a hot air drying furnace, aninfrared drying furnace, or the like.

The resin portions (positive electrode side resin portion 52 a andnegative electrode side resin portion 62 a) that can be formed on thepositive electrode current collector 51 and the negative electrodecurrent collector 61 are substantially formed of the swellable resindescribed above. As the swellable resin contained in the resin portion,a resin that has an excellent swelling property and a high thermalcapacity can be preferably used. As the swellable resin,polyvinylpyrrolidone (PVP), SBR, an acrylic resin and the like can beused, but the swellable resin is not limited to this. As the acrylicresin, for example, the acrylic binder that can be used as the binderfor the non-aqueous electrolyte secondary battery can be used.

The resin portion according to the present embodiment is substantiallyformed of the swellable resin described above, but may contain othercomponents as long as the effects of the present disclosure are notsignificantly impaired.

The resin portion can be formed by, for example, mixing the swellableresin in the aqueous solvent, applying the mixed solvent to the mixturelayer non-forming portion (at least any one of positive electrodemixture layer non-forming portion 52 and negative electrode mixturelayer non-forming portion 62), and drying the applied solvent.

The thermal capacity of the negative electrode side resin portion 62 athat can be formed on the negative electrode current collector 61 is notparticularly limited as long as the effects of the present disclosureare exhibited, but is, per unit weight (kg) of the negative electrodemixture layer 63, preferably 5 J/(kg·K) or more, more preferably 10J/(kg·K) or more, still more preferably 20 J/(kg·K). Further, thethermal capacity of the negative electrode side resin portion 62 a isnormally 50 J/(kg·K) or less per unit weight (kg) of the negativeelectrode mixture layer 63.

A weight of the negative electrode side resin portion 62 a that can beformed on the negative electrode current collector 61 is notparticularly limited as long as the effect of the disclosure isexhibited, but is normally 10% or less of the weight of the positiveelectrode mixture layer 53, for example, 5% or less, and more than 0%,for example, 0.1% or more.

The thermal capacity of the positive electrode side resin portion 52 athat can be formed on the positive electrode current collector 51 is notparticularly limited as long as the effects of the present disclosureare exhibited, but is, per unit weight (kg) of the positive electrodemixture layer 53, preferably 5 J/(kg·K) or more, more preferably 10J/(kg·K) or more, still more preferably 20 J/(kg·K) or more. Further,the thermal capacity of the positive electrode side resin portion 52 ais normally 50 J/(kg·K) or less per unit weight (kg) of the positiveelectrode mixture layer 53.

A weight of the positive electrode side resin portion 52 a that can beformed on the positive electrode current collector 51 is notparticularly limited as long as the effect of the disclosure isexhibited, but is normally 10% or less of the weight of the positiveelectrode mixture layer 53, for example, 5% or less, and more than 0%,for example, 0.1% or more.

The cycle resistance can be improved even in a case where the resinportion is provided on any of the positive electrode 50 and the negativeelectrode 60, but in a case where the resin portion is provided on anyone of the positive electrode 50 and the negative electrode 60, theresistance increase rate after application of the cycle can be moresuitably suppressed in a case where the resin portion is provided on thenegative electrode 60 side. Although not particularly limited, one ofthe reasons why the cycle resistance can be further improved byproviding the resin portion on the negative electrode 60 side ascompared with the positive electrode 50 side is considered that thenon-aqueous electrolyte 80 is likely to flow out from the electrode dueto the temperature rise in the negative electrode 60 as compared withthe positive electrode 50. That is, consideration is made that theeffect of suppressing the outflow of the electrolyte is high bysuppressing the temperature rise on the negative electrode 60 side.

It is preferable that the resin portion be formed along the mixturelayer. By disposing the resin portion as described above, thetemperature unevenness at the end portion of the electrode body can bereduced and the thermal capacity of the end portion of the electrodebody can be more uniformly improved. As a result, the non-aqueouselectrolyte 80 can be more suitably held in the electrode body 40, andthe high rate resistance of the lithium-ion secondary battery 100 can beimproved.

As the separators 72, 74, a porous sheet (film) made of polyolefin, suchas polyethylene (PE) or polypropylene (PP), is suitably used. Such aporous sheet may have a single layer structure or a stacked structure oftwo or more layers (for example, a three layer structure in which the PPlayers are stacked on both sides of the PE layer). A heat resistantlayer (HRL) may be provided on the surfaces of the separators 72, 74.

Then, the wound electrode body 40 is manufactured by winding thepositive electrode 50, the negative electrode 60, and the separators 72,74 described above according to a known method. Specifically, the woundelectrode body 40 can be manufactured by winding a stacked body in whichthe positive electrode 50 and the negative electrode 60 are overlappedwith each other via two separators 72, 74 in the longitudinal directionwith the axis WL as a winding axis, and pressing and bending the stackedbody to be flat in one direction orthogonal to the winding axis WL.

Typically, the non-aqueous electrolyte 80 contains a non-aqueous solventand a supporting salt.

As the non-aqueous solvent, various organic solvents, such ascarbonates, ethers, esters, nitriles, sulfones, and lactones that areused in the electrolyte of a general lithium secondary battery can beused without particular limitation. Specific examples thereof includeethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate(DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC),monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC),monofluoromethyldifluoromethyl carbonate (F-DMC), and trifluorodimethylcarbonate (TFDMC). Such a non-aqueous solvent can be used alone, or twoor more types thereof can be used in combination as appropriate.

As the supporting salt, for example, a lithium salt, such as LiPF₆,LiBF₄, and LiClO₄ (preferably, LiPF₆), can be suitably used. Aconcentration of the supporting salt is preferably 0.7 mol/L or more and1.3 mol/L or less.

In the lithium-ion secondary battery 100 configured as described above,deterioration due to repeated charging and discharging can besuppressed, and the battery performance can be further maintained for along period of time. The lithium-ion secondary battery 100 can be usedfor various applications. Examples of the suitable applications includethe power source for driving mounted on the vehicle, such as theelectric vehicle (EV), the hybrid vehicle (HV), and the plug-in hybridvehicle (PHV).

Next, the suitable embodiment will be described below with reference toexamples, but the present disclosure is not intended to be limited tosuch examples.

Manufacturing of Lithium-Ion Secondary Battery for Evaluation

Preparation of Paste and Swellable resin Mixture

The positive electrode mixture paste was prepared by mixingLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ (LNCM) as the positive electrode activematerial, acetylene black (AB) as the conductive material, andpolyvinylidene fluoride (PVdF) as the binder with N-methylpyrrolidone(NMP) at a mass ratio of LNCM:AB:PVdF=87:10:3.

The negative electrode mixture paste was prepared by mixing naturalgraphite-based carbon material (C) as the negative electrode activematerial, styrene-butadiene rubber (SBR) as the binder, andcarboxymethyl cellulose (CMC) as the thickener with ion-exchanged waterwith a mass ratio of C:SBR:CMC=98:1:1. Polyvinylpyrrolidone (PVP) as theswellable resin was mixed with ion-exchanged water at a mass ratio of10% to prepare a PVP solution.

Manufacturing of Electrode

Example 1

The positive electrode that has the positive electrode mixture layer wasmanufactured by applying the positive electrode mixture paste to thealuminum foil and drying the applied paste.

The negative electrode that has the negative electrode mixture layer wasmanufactured by applying the negative electrode mixture paste to thecopper foil and drying the applied paste.

Example 2

The positive electrode having the positive electrode mixture layer wasmanufactured by applying the positive electrode mixture paste to thealuminum foil and drying the applied paste.

The negative electrode that has the negative electrode mixture layer andthe negative electrode side resin portion was manufactured by applyingthe negative electrode mixture paste and the PVP solution to the copperfoil and drying the applied paste. The PVP solution was applied suchthat the thermal capacity of the negative electrode side resin portionwas 5 J/(kg·K) per unit weight (kg) of the negative electrode mixturelayer.

Examples 3 to 8

The positive electrode and the negative electrode were manufactured inthe same manner as in Example 2 except that the PVP solution was appliedsuch that the thermal capacity of the negative electrode side resinportion was the value shown in Table 1.

Example 9

The positive electrode and the negative electrode were manufactured inthe same manner as in Example 2 except that the applied amounts of thenegative electrode mixture paste and the PVP solution were 1.2 times theapplied amounts in Example 3.

Example 10

The positive electrode and the negative electrode were manufactured inthe same manner as in Example 2 except that the applied amounts of thenegative electrode mixture paste and the PVP solution were 1.2 times theapplied amounts in Example 6.

Example 11

The positive electrode that has the positive electrode mixture layer andthe positive electrode side resin portion was manufactured by applyingthe positive electrode mixture paste and the PVP solution to thealuminum foil and drying the applied paste. The PVP solution was appliedsuch that the thermal capacity of the positive electrode side resinportion was 20 J/(kg·K) per unit weight (kg) of the positive electrodemixture layer.

The negative electrode having the negative electrode mixture layer wasmanufactured by applying the negative electrode mixture paste to thecopper foil and drying the applied paste.

Manufacturing of Non-Aqueous Electrolyte

A non-aqueous electrolyte for testing was manufactured by mixingethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethylcarbonate (DMC) at a volume ratio of 30:40:30, and dissolving LiPF₆ asthe supporting salt at a concentration of 1.0 mol/L.

Manufacturing of Lithium-Ion Secondary Battery Lithium-ion secondarybatteries were respectively constructed by using the electrodes(positive electrode and negative electrode) of Examples 1 to 11, twoseparator sheets, and the non-aqueous electrolyte. As the separatorsheet, a separator sheet having a three layer structure made of PP/PE/PPwas used.

Specifically, the positive electrode, the negative electrode, and theseparator sheet were overlapped with each other, wound, and pressed fromthe side to manufacture the flat wound electrode body. In this case, thetwo separator sheets were disposed such that the surface on which theheat resistant porous layer was formed faced the positive electrodemixture layer. Then, the wound electrode body was accommodated in thebox-shaped battery case made of aluminum, the non-aqueous electrolytewas injected through an injection hole of the battery case, and then theinjection hole was sealed. As described above, the lithium-ion secondarybatteries respectively provided with the electrodes of Examples 1 to 11were manufactured.

Charge and Discharge Cycle Test

The lithium-ion secondary batteries of Examples 1 to 11 were subjectedto a charge and discharge cycle test in which charging and dischargingwere repeated at a high rate. Specifically, in an environment of 25° C.,a high rate charge and discharge cycle in which discharging is performedfor 150 seconds with a fixed current of 2 C, resting is performed for 10seconds, charging is performed for 10 seconds with a fixed current of 30C, and resting is performed for 10 seconds was repeated 1000 times.

By using an IV resistance (initial resistance of battery) before thecharge and discharge cycle test and an IV resistance after the chargeand discharge cycle test, the resistance increase rate (%) wascalculated by Equation 1 below.

resistance increase rate (%)=(IV resistance after charge and dischargecycle test−IV resistance before charge and discharge cycle test)/IVresistance before charge and discharge cycle test×100  Equation 1:

Further, the resistance increase rate (%) of each of Examples 2 to 11with respect to the resistance increase rate of Example 1 was calculatedby Equation 2 below. Table 1 shows the results.

resistance increase rate (%) with respect to resistance increase rate ofExample 1=resistance increase rate calculated by Equation 1/resistanceincrease rate of Example 1 calculated by Equation 1×100  Equation 2:

Here, “1C” means an amount of current that can charge a battery capacity(Ah) predicted from the theoretical capacity of the positive electrodein one hour. For the IV resistances before and after the charge anddischarge cycle was obtained by the inclination obtained by adjustingthe battery to SOC 60%, and charging the battery at 1 C, 3 C, and 5 Crespectively for 10 seconds in an environment of 25° C., and plotting avoltage drop value ΔV that is a value obtained by subtracting a voltagevalue at 10 seconds from an initial voltage value on a vertical axis byusing the measured current value as the horizontal axis.

TABLE 1 Thermal capacity Resistance increase J/(kg · K) of rate after1000 Electrode in which resin portion per cycles (ratio resin portion(resin unit weight of with Example Example layer) is formed mixturelayer 1 as 100%) 1 Without forming 0 100%  2 Negative electrode 5 98% 3Negative electrode 10 96% 4 Negative electrode 13 95% 5 Negativeelectrode 16 94% 6 Negative electrode 20 87% 7 Negative electrode 25 78%8 Negative electrode 28 73% 9 Negative electrode 10 95% 10 Negativeelectrode 20 88% 11 Positive electrode 20 93%

As shown in Table 1, as compared with the lithium-ion secondary batteryof Example 1 that does not have the resin portion in the positiveelectrode and the negative electrode, the lithium-ion secondarybatteries of Examples 2 to 11 having the resin portion in the positiveelectrode or the negative electrode had a low resistance increase rateafter the high rate charge and discharge cycle (hereinafter, simplyreferred to as the “resistance increase rate”). It can be seen that theincrease in resistance can be suppressed by disposing the swellableresin in the mixture layer non-forming portion.

Further, in Examples 1 to 8, the resistance increase rate was decreasedas the thermal capacity of the resin portion with respect to the unitweight of the mixture layer was increased. It can be seen that theincrease in resistance can be more suitably suppressed by increasing theamount of the swellable resins to be disposed and increasing the thermalcapacity of the resin portion. In the comparison between Example 3 andExample 9 and the comparison between Example 6 and Example 10, in a casewhere the thermal capacity of the resin portion was the same, theresistance increase rate did not change much even in a case where theweight changed. It can be seen that the resistance increase rate islargely contributed by the thermal capacity of the resin portion.

In the comparison between Example 6 and Example 11, the resistanceincrease rate was low in a case where the resin portion was provided onthe negative electrode side as compared with a case where the resinportion was provided on the positive electrode side. It can be seen thatin a case where the resin portion is provided on any one of the positiveelectrode side and the negative electrode side, the effect of decreasingthe resistance increase rate is high in a case where the resin portionis provided on the negative electrode side as compared with a case wherethe resin portion was provided on the positive electrode side.

From the above, with the lithium-ion secondary battery disclosed herein,the resistance increase rate after the high rate charge and dischargecycle can be suppressed, and the high rate resistance can be improved.

Specific examples of the present disclosure have been described indetail above, but these examples are merely examples and do not limitthe scope of claims. The disclosures disclosed herein include variousmodifications and changes of the specific examples.

What is claimed is:
 1. A non-aqueous electrolyte secondary battery comprising: an electrode body that has a structure in which a plurality of positive electrodes and negative electrodes are stacked via a separator; and a non-aqueous electrolyte, wherein: the positive electrode includes a positive electrode mixture layer in which a mixture containing a positive electrode active material is formed and a positive electrode mixture layer non-forming portion in which the positive electrode mixture layer is not formed; the negative electrode includes a negative electrode mixture layer in which a mixture containing a negative electrode active material is formed and a negative electrode mixture layer non-forming portion in which the negative electrode mixture layer is not formed; and at least one of the positive electrode mixture layer non-forming portion and the negative electrode mixture layer non-forming portion has a resin portion substantially formed of a swellable resin having a property of swelling the non-aqueous electrolyte.
 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin portion is formed along the corresponding mixture layer.
 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein a thermal capacity of the resin portion is 10 J/(kg·K) or more per unit weight of the corresponding mixture layer.
 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin portion contains at least any one of polyvinylpyrrolidone, styrene-butadiene rubber, and an acrylic resin.
 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin portion is formed at least in the negative electrode mixture layer non-forming portion. 